Diverse types of crashboxes for bumper systems of motor vehicles are known. The crashbox is arranged between a bumper or a bumper crossmember and a vehicle or a vehicle longitudinal member. In order to protect the motor vehicle frame from pushing and/or shearing forces which are introduced into the crashbox via the bumper or the bumper crossmember in the event of a collision, the crashbox limits the transmitted force components to a value that is not harmful for the motor vehicle frame by converting the kinetic energy into heat and into internal material stresses by the plastic deformation of the crashbox. The joining points of the crashbox to the frame and to the bumper or bumper crossmember and to the vehicle or the vehicle longitudinal member are maintained here during the appropriate deformation of the crashbox.
In addition to tubular crashboxes with an annular or a polygonal cross-sectional area, which serve for the absorption of pushing and/or tensile forces and are manufactured, for example, as extruded profiles or pultrusion profiles from fiber-filled plastics or from an aluminum alloy, use is made of crashboxes of box-shaped or conical configuration in a shell-type construction which, in comparison to the tubular crashboxes, have greater resistance to transverse forces or bending moments and therefore a greater buckling strength.
In the case of the tubular crashboxes, a virtually uniform absorption of force can be achieved by the chip-removing or severing cutting of the casing body and also by turning over the casing surface of the crashbox from the inside to the outside over the length of the crashbox. In the case of the box-shaped or conical crashboxes, the absorption of force takes place by compression and extension of the casing body of the crashbox, wherein, as a result of bumps and dents formed in a regular arrangement in the casing, said casing creases during deformation. Beads and/or pressure release openings in the casing surface of the crashboxes permit a reduction in the component mass and serve for the intended or uniform deformation of the crashbox, wherein both the speed-dependent deformation properties of the material and of the joining points are to be taken into consideration and the unintended production of cracks or the breaking up of the crashbox are to be avoided.
A crashbox is thus described, for example in DE 10 2004 013 712 A1, in which the upper and lower walls of the crashbox converge continuously towards each other from a flange, with which the crashbox can be fastened to a vehicle crossmember, until said walls encounter the bumper crossmember, to which the crashbox is likewise fastened.
Furthermore, DE 100 14 469 A1 discloses a box-shaped crashbox in which the upper wall and lower wall, on the one hand, and the side walls, on the other hand, are arranged parallel to one another over the entire longitudinal extent of the crashbox.
DE 2005 053 778 A1 likewise describes a crashbox in which the upper wall and the lower wall converge towards each other over the entire longitudinal extent of the crashbox.
In all of the known designs of crashboxes, a satisfactory conversion of kinetic energy into heat or deformation energy as a consequence of a collision of a motor vehicle equipped with a crashbox of this type is indeed achieved. However, it has been shown that, under some circumstances, an asymmetrical deformation of the crashbox takes place, in particular in the vertical direction, and, in the extreme case, the crashbox walls even tear. This in particular occur in the case of a height offset between bumper, on the one hand, and vehicle longitudinal member, on the other hand.